1. Field of the Invention
This invention relates to multilayer metallized films which have selective energy transmission and reflection characteristics. More particularly, it concerns improvements to energy reflective/transmissive metal/dielectric films which lead to improved durability and corrosion resistance for such films.
2. Description of the Prior Art
Since at least the 1950's efforts have been made to come up with materials which will selectively interfere with the passage of particular types of energy. For example, there are numerous applications where one wishes to allow visible and near infrared light to pass though a material while retaining far infrared radiation (heat). These materials find application in the areas of architectural glazings, furnace windows, goggles, and automotive glazings. Similarly, there are other applications where one desires to allow visible light to pass while blocking the passage of radio frequency waves or other forms of electromagnetic radiation. These materials find application in the areas of high security architectural glazings, CRT shields, and the like.
Over the years the sophistication of these products has increased dramatically. In the area of heat rejection, early work focussed on absorbing the heat and preventing its transmission. Pigments and dyes were added to the body of glazing materials to accomplish this. Metallic wires were embedded or applied to glazing sheets and then grounded to act as RF shields and the like.
More recently, it has been realized that one can apply thin films of metals to the surfaces of materials to achieve selective energy transmission. If these films are properly chosen they can serve as selective reflectors of certain types of electromagnetic radiation while transmitting others.
In the area of using metallic films as transparent heat reflectors, there has been substantial effort directed toward the use of multilayer films. Workers such as John C. C. Fan et al. in U.S. Pat. No. 4,337,990, pointed out that one could improve the overall selectivity of metallic films by accompanying them by one or more nonmetallic layers. These nonmetallic layers typically were inorganic metal compounds (i.e., dielectric materials) and were variously referred to as "antireflection layers," "phase matching layers" and the like.
Southwall Technologies Inc. has commercialized a range of products which include one or more transparent metal layers bounded on one or both sides by a dielectric layer. These materials have been developed for use as heat reflectors for window glazings and as radiation and interference shields for CRT's and other types of electronic equipment. While this type of product can be adapted to a wide range of applications, we have found that in certain settings, particularly settings which present a corrosive environment, the longevity of this type of metal/dielectric product could be improved.
This invention addresses this longevity problem and is directed to improving these metal/dielectric coatings and particularly coatings based on silver or copper metal in combination with indium- and/or zinc-based dielectrics.